The present invention relates to power factor correction (PFC) converters, and more particularly to interleaved PFC converters.
Electric power is distributed almost universally in an alternating current (AC) format that allows for efficient transmission. Most devices however, including personal computers, televisions, etc., require direct current (DC) power. Power supplies act to convert the AC input supplied by a line to a DC output suitable for consumption by a device or load. A switched-mode power supply (SMPS) employing a boost regulator is commonly employed in this role of AC-to-DC power conversion. A benefit of employing a SMPS having a boost regulator topology is the boost regulator can be controlled to provide power factor correction. Subsequent stages may be employed to step-down the output of the PFC boost regulator to a desired DC output voltage.
A boost regulator includes an inductor connected between a rectified input and the DC output. A shunt switch is selectively controlled to charge the inductor (during ON times of the switch) and to discharge the inductor to the DC output (during OFF times of the switch).
The power capability of an interleaved AC-to-DC converter may be increased by connecting PFC boost regulators in parallel with one another and switching them out-of-phase with one another in an interleaved manner to provide the desired output. Connecting the PFC boost regulators in parallel results in each boost circuit carrying half the current of a single boost regulator circuit. As a result, conductions losses—which are proportional to the square of the current through each parallel connected boost regulator—are cut in half as compared with a single boost regulator circuit. However, the addition of one or more parallel-connected PFC sub-circuits results in additional switching losses associated with having to turn ON and OFF one or more switches associated with each boost circuit. If the switching losses exceed the conduction losses, it may be beneficial to turn OFF one or more phases of the parallel connected PFC regulators. However, determining at what point it is desirable to turn ON or OFF a phase is difficult to determine at various operating points.